I have this percussion massager: https://www.amazon.com/dp/B00JDUFOAE it is an older model, no longer made, but they have others. I pulled it out last night after reading this. I don't get much out of it and never did. A yoga teacher "commanded" me to get this 15 years ago. These "machines" are no comparison to the focussed work you would do with a lacrosse ball, theracane, foam roller, Armaid, etc, or that a therapist would do to you with hands, knuckle, elbows. I would definitely recommend instead get an Armaid. And all of Starrett's books are good. His first one is Becoming a Supple Leopard: https://www.amazon.com/dp/1628600837/ These are expensive books, but quite worthwhile - note the reviews. And absolutely get Sharon Butler's book: https://www.amazon.com/dp/1572240393/ Her website: http://www.selfcare4rsi.com/

Part of the deep tissue massage thing is releasing deep chronic stored tension. But equally important is freeing stuck fascia. So Starrett calls this "smashing and flossing". Working back and forth against the "grain" of muscle tissue to unglue it and restore movement where tissues are supposed to slide across each other. Long-term chronic tension results in the fascia sticking and gluing things together if they are no longer moving.

Chinese Proverb - Moving door does not have rusted hinges.

Chinese Proverb: When healing patient - better not to use knife.